Jupe's impression of Hitchcock, and his horrified, indignant reaction.
Jupe's response to Skinny and his dead rat.
"I can understand your desire to see justice done, Skinny...for I see that the victim was one of your best friends."
"My preliminary examination...suggests that he probably died of indigestion brought on by trying to swallow the bragging of someone whose identity, at the moment, must remain concealed behind the initials E.S.N."
Pete getting caught in the grapevine ("an unusually vicious specimen" according to Jupiter), particularly Jupiter's explanation afterward. "It was a very evenly matched test. Neither of you was using any intelligence. The vine doesn't have any, and you allowed panic to cloud your mental process."
Jupe shoving Freeman in the mummy case and sitting on it.
Jupe's trick with the walkie-talkies, using his to listen in on Bob and Pete's conversation about the letter from Professor Yarborough so he can supposedly deduce the letter and its contents without their telling him anything. Made funnier that it's a bit of revenge for Pete and Bob doing the same thing to him, "deducing" how he ended up in the state he was in after spying on him through the See-All.
Jupiter breaking out of the chair: "Jupe! What's wrong? Are you in a fight or something?" "I am fighting an enraged chair. And I think I'm winning."
Like the example above, Jupe's "mind-reading" of Bob to explain what happened to the plaster bust he and Hans brought back (because Jupiter was being held captive by the villains at the time and could hear everything they told their partner to do over their CB radio).
Aunt Mathilda vs. Farrier—refusing to let him get a word in edgewise, interfering with his flirting with Mrs. Dobson, shooting down his lame attempt to strike up a conversation with her, and afterward calling him "a silly ass." Also, her marveling at Mrs. Dobson having a baseball bat for intruders, while Jupiter thinks she'd use a bureau.
And the scene where Kaluk is sitting in the library of Hilltop House as if about to be served at a restaurant, only for Demetrieff to give him a hot dog he roasted over the fireplace; his disgusted expression is priceless.
All of Pete's snarky asides while watching Jay Eastland and his film crew and actors.
Mara staring down Aunt Mathilda...and winning. "Mara did have gifts."
The "jewels" in the mattress in the old adobe, which turn out to be a collection of nuts belonging to a ground squirrel.
During the chase after the shed is set on fire, Pete tackles Jupe, thinking he's Java Jim; Pete is mortified, Jupiter is...less than pleased. Bob thinks it's hilarious.
It happens again in Purple Pirate, except this time Bob also leaps on Pete so all three end up struggling wildly together.
The key being hidden under the bed Havemeyer and fake Anna were sleeping in.
Bob mocking Jupiter's incipient Sherlock Scan. "In the Sherlock Holmes stories, the great detective finds a collar button and immediately he can tell all about the suspect, including the fact that he was born in Ireland and that he likes kippers with his tea. You have a matchbook which is doubtless a priceless clue. Tell us about Harold Thomas!"
Bob and Jupiter throwing tennis balls at Pete after one too many iterations of "I'm hungry/I need lunch."
Jupiter trying to plan the entirety of their Magic Mountain excursion for "covering the most rides in the least time", with increasing complexity in trying to account for long lines, rides being out of commission, repeat rides, and so forth...until Pete and Bob get exasperated and say, "Can't we just go wherever we feel like, and actually have fun?" Jupiter is offended at first...then just shrugs, throws the plan aside, and laughs too.
Aside from Hitchcock's horror in the introduction about there being two Jupiter Joneses, there's the part from the end of the book when he names the case while making the same point to the boys. Jupiter naturally doesn't find it very funny, but Bob and Pete do. (It's also totally in character for Hitchcock, even with him having come to respect Jupiter greatly by that point.)
Jupiter thinking antennae were going to grow on Woolley's head.
After Mr. Andrews tells Bob he needs to stay with him to do some interview transcription, Bob says, "I guess the fellows can manage awhile without me." Pete then responds, "Gosh, you really think we can, Records?" (gets spoon thrown at him)
Pete: I'll wait with Bob. I'm allergic to guys who might get nasty.
Pete: I'm only ambitious. My ambition is to live until I am very, very old.
After Jupe has figured out what the villains' plan is and confides it to the Barrons, they go to meet the "aliens" in order to flush them out and trap them. Instead of bringing gold to the "UFO", Mr. Barron brings...the book he's writing, while his wife brings her wedding dress and family photos. The reaction of the "aliens" is priceless.
Pete, sneaking around the Purple Pirate Lair from the abalone factory pier, discovers he has to swim across the cove to stay out of sight. He lowers himself along a rope, nerves himself, and discovers...in his own words "a death-defying plunge into an inch of water."
Jupe getting stuck on the roof of Evans' tower and, like a cat, being afraid to come back down. "I am not climbing back down on that route for midgets and flies...as far as I am concerned, I am ready to live up here permanently. You may ask Aunt Mathilda and Uncle Titus to send up some food and my bed!"
Wandering Cave Man
In a Villain Ball fashion, but it's rather hilarious that not only does Dr. Hoffer get found out because, being a scientist, he couldn't help but want to be accurate when posing as a cave man by being barefoot (never mind the costume he wears being not at all accurate, as the resident anthropologist points out), but the specific detail that trips him up: not just that modern, shoe-wearing people do not have spread-out feet the way someone used to going barefoot all their lives would, but that he has a hammer toe.
This bit, when the boys are trying to get Fluke into a makeshift pit they've fashioned to keep him in water until they can bring adult rescuers. Pete remarks rather pointedly that he hopes Jupiter will do his part to help them.
Jupe didn't bother to answer him. It seemed to him he had already done more than his share. The whole plan had been his idea.
The boys' act to get out of more work in the salvage yard, where they feign being so weak from hunger that they can't even walk. It's so funny it makes Aunt Mathilda herself burst out laughing.
Worthington standing up to Mr. Temple and the police, and defending Jupiter from the former, is both awesome and hilarious, and contrary to the OOC bit on the main page, superbly in-character.
Trail of Terror
Pete's grandfather's snoring is extremely loud, but when Bob claims he has a sinus problem, Pete offers his mother's analysis: "He doesn't like to be ignored, even when he's unconscious."
Jupe actually becomes briefly shy and starstruck over the idea of getting to work with the FBI. note It would seem he'd forgotten about getting to do so in Deadly Double, except for most of that book he was either kidnapped or working exclusively with the Nandan agents; the Feds only get involved briefly near the beginning and again near the end. Also, while that case did have very serious international repercussions, this would be the first time the Three Investigators became involved in something which, as Jupiter points out, specifically affects national security.